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Title: Rate-limiting step of proton transport in liquid water
Plain: Extra hydrogen ions move through water several times faster than other ions by hopping between water molecules. Which molecular step sets the speed of this hopping is not agreed.
Precise: For an excess proton in liquid water at $300\,\mathrm{K}$, identify the rate-limiting step of structural (Grotthuss) diffusion, the relay of the proton from molecule to molecule: hydrogen-bond breaking or forming in the second solvation shell, or motion along the proton-transfer coordinate. An answer is a simulation with path-integral nuclei on a near-quantum-chemical potential that reproduces the measured proton diffusion coefficient (about $9.3e-5\,\mathrm{cm}^2/\mathrm{s}$) and its H/D isotope effect and identifies the step from the trajectories.
Settled by: Path-integral molecular dynamics on a coupled-cluster-quality potential reproducing diffusion and isotope effect, with a committor or rate analysis of the transfer events.
Kind: well-posed
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: (empty)